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Bedrock Dewatering for Construction of Marmet and Soo Lock Projects

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Bedrock Dewatering for Construction of Marmet and Soo Lock Projects Bedrock Dewatering for Construction of Marmet and Soo Lock Projects Michael Nield Engineering Geologist Dam Safety Production Center, Huntington, WV August 2012 US Army Corps of Engineers BUILDING STRONG® BEDROCK DEWATERING FOR CONSTRUCTION OUTLINE 1. Marmet Lock Replacement Project (construction) - Project Description - Site Geology - Permeability and Groundwater Inflow - Dewatering Provisions 2. Soo Lock Replacement Project (design) - Project Description - Site Geology - Permeability and Predicted Groundwater Inflow - Impact to Design BUILDING STRONG® MARMET LOCK - PROJECT DESCRIPTION . Located on Kanawha River, OHIIO RIVER near Charleston, West GREAT LAKES DIVISION Virginia. Permits economic river transportation of coal, MARMET aggregate and chemicals. LOCKS & DAM . Construction of the new replacement lock was completed in 2009 BUILDING STRONG® “Busiest Lock in USA” Prior to New Lock Twin 56’ X 360’ Chambers Completed in 1934 Aerial View – Original Locks BUILDING STRONG® New 110’ X 800’ Lock Chamber Original Locks New Guard Wall New Guide Walls Aerial View – New Replacement Lock BUILDING STRONG® MARMET LOCK - SITE GEOLOGY . 157 TOTAL BORINGS . 10,200’ TOTAL DRILLING . 3,700’ ROCK CORE . 294 PRESSURE TESTS Subsurface Exploration – Boring Location Plan BUILDING STRONG® General Geology . Soil thickness 40 to 60 feet . Relatively flat top of rock surface at elev. 552 ± 3’ . Sedimentary rock of the Pennsylvanian-aged Kanawha Formation Sandstone member (23 to 43 feet thick) Shale member (19 to 33 feet thick) . Low angled bedding with 0o-10o dip to the Northwest . Slightly fractured with occasional high angled joints (70o-90o) BUILDING STRONG® Bedrock Units - Sandstone Member . Light gray . Moderately hard to hard . Medium to fine grained . Average unconfined compressive strength 8,442 psi . Foundation for lock walls . Occasional thin coal seam or zone of carbonaceous stringers BUILDING STRONG® Bedrock Units - Shale Member . Gray to dark gray . Moderately hard to soft . Silty . Average unconfined compressive strength 6,678 psi BUILDING STRONG® Geologic Cross Section - During Construction Anchored Anchored Retaining Existing Wall Landwall 600 600 550 550 500 500 -100 0 100 SOIL SANDSTONE WEAK SEAMS SHALE Geologic Cross Section – Chamber Monoliths BUILDING STRONG® MARMET LOCK – BEDROCK PERMEABILITY Pressure Testing PRESSURE GAUGE WATER LINE WATER METER VALVE BORE HOLE BLADDER OPEN DISCONTINUITIES BEDROCK 5’ BUILDING STRONG® Pressure Testing . Measure water flow while maintaining predetermined pressure, typically recorded in gal/min, CFM. Values are often converted to Lugeons OPEN DISCONTINUITIES BEDROCK BUILDING STRONG® Hydraulic Conductivity . 294 individual pressure tests in 36 holes located within cofferdam. Convert pressure testing results to Hydraulic Conductivity value K using equation from USBR: K = Q/2πLH loge(L/r) (Q=flow, L=length tested, H=pressure, r=hole radius) . Convert pressure test data to Lugeon then convert to Hydraulic Conductivity K: K = Lu x 10-7 (1 Lugeon equals one liter per minute per meter hole at a pressure of 10 bars) BUILDING STRONG® Hydraulic Conductivity – Groundwater Inflow . Average permeability or Hydraulic Conductivity (K) value from pressure testing results at Marmet is 1.69X10-6 m/s (5.54x10-6 ft/s), which is typical for sandstone. Average Hydraulic Conductivity values in bedrock increased when overlying soil was removed during construction at both Marmet and Winfield projects. Hydraulic Conductivity, along with known hydraulic gradient and excavated surface area can be utilized to help develop preliminary estimate of groundwater inflow during construction (using Darcy’s law). Calculated inflow from average K value is 520 gal/min and upper bound inflow value is 7,000 gal/min. BUILDING STRONG® Permeability Comparison – Logarithmic Scale 10-3 SOIL DEWATERING DESIGN VALUE 10-4 MAXIMUM TEST VALUE 10-5 10-6 MEAN TEST VALUE 10-7 CALCULATED 10-8 RANGE PUBLISHED RANGE 10-9 HYDRAULIC CONDUCTIVITY K (M/S) MARMET MARMET WINFIELD SANDSTONE DODSON-STILSON PRESSURE TESTS PRESSURE TESTS TYPICAL (Brassington, 1988) BUILDING STRONG® MARMET LOCK – DEWATERING PROVISIONS . Accurately portray bedrock conditions in contract documents, alerting the contractor to potential dewatering concerns and work effort. Graphic Logs of Borings Geologic Sections Geologic Mapping Geotechnical Baseline Report . Address in the specifications groundwater concerns during construction and provide appropriate bid items for compensation. Dewatering Grout Curtains Concrete Placement Anchor Installation BUILDING STRONG® Graphic Logs of Borings – Indicators of Permeability . QUANTIFY DESCRIPTIVE TERMS IN LEGEND . INCLUDE DOWN-HOLE CAMERA IMAGES IF TOP OF ROCK AVAILABLE AND DEPTH OF WEATHERING DRILL WATER LOSS BEDDING PLANE SPACING PRESSURE TEST DATA FRACTURES IRON STAINING RQD SEAMS BUILDING STRONG® Existing Foundation Maps – Indicators of Permeability . Fracture orientation, spacing, length and aperture . Foundation grout takes . Records of groundwater seepage and control methods EXCAVATION FOR NEW LOCK – IN THE DRY 28.5’ ORIGINAL CONCRETE LOCK WALL - COFFERDAM 56’ ORIGINAL LOCK CHAMBER – KANAWHA RIVER Original Lock Chamber and Lock Wall BUILDING STRONG® Existing Foundation Maps – Indicators of Permeability . Fracture orientation, spacing, length and aperture . Foundation grout takes . Records of groundwater seepage and control methods 5” WIDE CREVICE FRACTURE LENGTH +70’ 1.2’ WIDE CREVICE 0.4’ WIDE 0.05’– 0.1’ WIDE OPEN 0.05’- 0.1’ WIDE 0.03’ WIDE OPEN 0.0’– 0.1’ WIDE 0.7’– 1.0’ WIDE 0.05’ WIDE Original Lock Chamber and Lock Wall BUILDING STRONG® Groundwater Flow Through Fractures Fractures are the primary mechanism for bedrock groundwater inflow into an excavation. Groundwater flow can be estimated through individual bedrock fractures utilizing the following equation (maximum value – does not take into consideration joint roughness, shape, infilling, laminar flow etc.): 3 q = γw/12µw e i (q=flow, γw=unit weight of water, µw=dynamic viscosity of water, e=fracture aperture, i=hydraulic gradient) BUILDING STRONG® Cofferdam – Construction of New Lock – Aerial View Cofferdam (sheet pile cells and original lock) Slurry Wall and Relief Wells Soil Retaining Wall New Lock Chamber BUILDING STRONG® Cofferdam – Construction of New Lock – Rock Excavation Original Lock Sheet Pile Cells Soil Retaining Wall BUILDING STRONG® COFFERDAM: Barge Tow ORIGINAL LOCK KANAWHA RIVER 553 Anchors SANDSTONE NEW LOCK MEMBER FOUNDATION Hydraulic gradient ranges 531 from 0.13 to 1.2 523.2 Uplift pressures measured SHALE using piezometers during MEMBER construction – found to be as anticipated or less. Cofferdam – Hydraulic Gradient & Uplift BUILDING STRONG® Specifications – Dewatering Bedrock Groundwater . “The Dewatering Systems shall be designed and operated so as to allow construction of the lock chamber to be accomplished essentially in the dry, as well as to facilitate construction of all other project features.” . “The Contractor's Dewatering System shall be designed in order to control groundwater, surface water, and incidental water, including seepage through the rock foundation… . “…and then sumping the remaining groundwater and any other seepage into the bottom of the excavation.” . “…dewatering facilities and supplemental dewatering facilities that may be required to control any seepage from excavated slopes or into the bottom of the excavation...” . “Supplemental measures may include the installation of wellpoints, inverted filters, french drains, relief wells drilled into either soil or rock, and appropriate pumps, piping, and appurtenances as necessary…” BUILDING STRONG® Control Groundwater Seepage – Concrete Placement “Rock surfaces upon which concrete is to be placed shall be clean and free from oil, standing or running water, ice, mud, drummy rock, coatings, debris, and loose, semi-detached, overhanging, or unsound fragments.” BUILDING STRONG® Control Groundwater Seepage – Foundation Treatment Profile – Prior to Concrete Lift Placement BUILDING STRONG® Control Groundwater Seepage – Foundation Treatment Profile – After Concrete Lift Placement BUILDING STRONG® Control Groundwater Seepage - Foundation BUILDING STRONG® Isolate Groundwater Seepage from Mass Concrete Placement BUILDING STRONG® Dewater and Control Groundwater Seepage Primary Discharge Pump Control of Seepage - Sidewalls Sand Bags & Sump Pump BUILDING STRONG® Provisions in Specifications Concerning Artesian Pressure Control Artesian Pressures: . Grouting for Foundation Anchor Installation . Foundation Drilling and Grouting BUILDING STRONG® Foundation Drilling and Grouting . Grout Curtain Inhibits Groundwater Flow Into Lock Chamber . Grout Curtain Extends to Elevation 510 . 10’ Spacing Between Primary and Secondary Holes . Optional Tertiary and Higher Order Holes BUILDING STRONG® Top of Rock Surface Gravel Filter at Base of Retaining Wall Know Location of Top of Rock Surface: . Sheet Pile Driven to Rock – Cofferdam & Retaining Wall . Seepage Cutoff Wall Through Soil – Key into Rock BUILDING STRONG® BEDROCK DEWATERING FOR CONSTRUCTION OUTLINE 1. Marmet Lock Replacement Project (construction) - Project Description - Site Geology - Permeability and Groundwater Inflow - Dewatering Provisions 2. Soo Lock Replacement Project (design) - Project Description - Site Geology - Permeability and Predicted Groundwater Inflow - Impact to Design BUILDING STRONG® SOO LOCKS – PROJECT DESCRIPTION SOO LOCKS . Located in Michigan’s Upper OHIIO RIVER Peninsula at Sault Ste. Marie GREAT LAKES DIVISION and
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